A new display language is three separate settings: the interface, the formats and the system locale for non-Unicode programs. Only the last one needs a reboot and fixes garbled old apps.
Install the pack with **Install-Language**, set the interface with **Set-WinUILanguageOverride** and the non-Unicode code page with **Set-WinSystemLocale**. Removing the old language is a separate step.
On a current build **Install-Language** pulls the whole pack. Without it only the keyboard layout and formats get added, and the interface stays English.
Install-Language -Language de-DE
Get-WinUserLanguageList | Select-Object LanguageTag,Autonym,InputMethodTips**Set-WinUILanguageOverride** changes the interface for the current user. It takes effect at the next sign-in, not immediately.
Set-WinUILanguageOverride -Language de-DE
Get-WinUILanguageOverrideThis is the setting behind **Region > Administrative > Language for non-Unicode programs**. Old installers and legacy apps use it; nothing else fixes their garbled text.
Set-WinSystemLocale -SystemLocale de-DE
Get-WinSystemLocale
:: requires a rebootDates and numbers follow **Set-Culture**, which is per user. A machine with German UI and US date format is this setting, not the display language.
Set-Culture -CultureInfo de-DE
Get-Culture | Select-Object Name,DateTimeFormat,NumberFormat
Set-WinHomeLocation -GeoId 94Read back the override, the system locale and the culture. Three green values are the whole check; a sign-in screen in the old language means one of them did not apply.
Get-WinUILanguageOverride
Get-WinSystemLocale
Get-Culture | Select-Object Name
Get-WinUserLanguageListDeleting the pack while it is still the fallback leaves a half-translated interface. Set the new language as the only entry, then uninstall the old capability.
$l = New-WinUserLanguageList de-DE
Set-WinUserLanguageList $l -Force
Uninstall-Language -Language en-US
Get-InstalledLanguageThe language pack is installed but its features are not. Install the full pack again, and check Get-InstalledLanguage for the LanguageFeatures entry.
Language packs come from Windows Update. Mark the connection as unmetered or use an ISO as the source for the optional features.
That is the system locale, not the display language. Set it with Set-WinSystemLocale and reboot.
The default account and the welcome screen keep their own language. Set it in the copy settings of the regional settings dialog.
Only if you add the layout to the user language list. The physical layout stays until you switch it, with the layout indicator in the taskbar.
Yes, and it is often the better choice: English interface with German number and date formats is one setting apart.
Set-WinUILanguageOverride and -WinSystemLocale back to the previous values, restore the culture with Set-Culture, then reinstall the old language pack and sign out.
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